I am on my 4th Brett experiment and right now the yeast in the batch I have is from bottle dregs. There is Brett in there, I don’t know much much I pitched, but it is a farmhouse ale with Brett. I recently read the gravity and it was at 1.002. Brewed 2 weeks ago and Still bubbling, though has slowed down and burps every 30 seconds now. I do not plan on transferring this beer, but I already taste a Brett character. When I stop seeing bubbles in the carboy I will bottle, a week ago I could see slight movement inside, the beer is beginning to clear up.
In the past I have pitched Brett into secondary. It took about a month for a pellicle to form on both of those beers, and then I waited another 5-6 months to bottle, those beers turned out fine, no autolsys.
I used the dregs from those beers to make another beer and the results were not as good. Thp. Applely. The beer is 8 months old now and I bottled it 3 months after fermentation. The thp has gone away and the beer has changed over time. I crack a bottle every once in a while and the results vary. That beer has more going on with it than I really know. (Not one bottle bomb, yet)
Personally I don’t think a primary Brett pitch with another strain is bad, from my experience. I just had more than Brett in my beer when I did it.
Eventually the Brett is going to eat away at all the sugars, so to get to your question about a cleaner beer if Brett is in secondary. I personally think yes, you can taste the 3711 and the Brett if you pitch Brett in secondary. I don’t taste the primary yeast that was in my built up from dregs experiments.
I have never had an autolysis issue with a primary pitch of Brett or a secondary. But I also don’t have tons of experience with Brett.